The invention relates to a transfer line transferring workpieces along a series of machining stations.
In the production of workpieces involving metal cutting operations it is common to use transfer lines which are adapted for the machining of a particular type of workpiece or for machining a limited number of similar types of workpieces. The transfer line is equipped with machining work stations through which the workpieces pass in series, in a predetermined sequence.
At each of the machining work stations, machining devices perform special machining operations on each workpiece that passes through the station.
The particular workpiece that is being machined is securely retained in a suitable device during the machining operation and is then transported by a transfer system to the next station. Depending on the type of the transfer line and its intended use, the workpiece retaining devices are either of a first unfixturized type that are fixed in position, or are of a second type comprising pallets which move through the transfer line fixed to the workpiece.
In order to ensure unobstructed workpiece access by the machining devices the unfixturized workpiece transfer method is often preferred over the pallet-type method, especially when the workpiece to be machined has a relatively intricate configuration.
This is particularly true in the case of metal cutting machining operations performed on differential housings that are used as driveline components in automobiles. These housings must be machined, successively, from at least four different directions which are oriented at right angles relatively to one another. In order to ensure a close tolerance dimensional accuracy, the workpieces must be clamped in each of the machining work stations, and close tolerances must be held each time. The equipment of the machining work station usually remains unchanged since individual adjustment of each station to each workpiece passing through the station would not be desirable in terms of economy and efficiency.
One prior transfer line for the machining of differential housings is of the type in which the machining stations are interlinked by an overhead transfer system. The individual machining stations, which are provided with horizontally oriented as well as vertically suspended machining spindles, are equipped with stationary work rests into which the workpieces are deposited and retained by clamping devices during the machining operation.
In order to enable machining operations to be carried out from all sides of the workpiece, horizontally positioned machining spindles are placed at varying angles relative to the transfer direction. Some of the machining stations are positioned at a right angle relative to the transfer direction, whereas others are positioned at a 45.degree. angle. This requires that the particular workpiece to be machined must be turned several times by the transfer mechanism about its vertical axis and be inserted into the work rest at a corresponding angular position. The work rests are each provided with two locating surfaces which are oriented at right angles to one another and are inclined at an angle of 45.degree. relative to the horizontal axis.
The positioning of the machining stations at varying angles with respect to the transverse direction not only results in an irregular arrangement of the transfer line and the need for extra space, but it also makes it difficult, because of the inclined positioning of some of the machining stations, to locate a transfer mechanism below the conveying level of the workpieces. It is for that reason that an overhead transfer system must be used which, in turn, impedes the access to the workpieces from the top. This makes it necessary to equip the machining stations with vertically suspended tool machine spindles with specially designed and costly mechanisms for the transport of the workpieces to and from the machining stations.
In recognition of the foregoing limitations, it is the object of the present invention to provide a transfer line which is characterized by a simple and open configuration by its reduced space requirements, and by the fact that the machining operations on the workpiece can be carried out with the required precision.